Incorrect syntax highlighting in containers-transports.5

[mtrmac]

At least the https://github.com/containers/image/blob/main/docs/containers-transports.5.md#containers-storagestorage-specifierimage-iddocker-referenceimage-id paragraph does not consistently differentiate between [] literals and [] metacharacters; that makes the description unusable.

(The recommendation for users would still be to fish out the right value from a podman --log-level=debug log instead of trying to construct one with exactly the right paths and options manually, but having the reference correct is still valuable.)